Field of the Invention
The present invention relates to a composition having a very high proportion of 2-ethylhexyl silicate and to a specific process for preparation thereof, wherein ethyl silicate is transesterified with 2-ethylhexanol in the presence of a nonacidic catalyst and then the free alcohol is removed from the reaction mixture.
Discussion of the Background
Alkyl polysilicates, also called alkyl silicates, can be represented according to chemical understanding by general formulae including RO—[(RO—)2Si—O]n—R and [—Si(—OR)2O2/2-]n, with n>1 and R=alkyl, and have long been known as such, for example in the form of what is called ethyl silicate.
DE-B 1010739 teaches the preparation of polysilicic esters by reaction of tetraethoxysilane with higher alcohols such as cyclohexanol, methylcyclohexanol and phenols in the presence of an anhydrous or aqueous carboxylic acid as condensing agent, for example acetic or formic acid. The volatile compounds formed in the reaction, such as lower alcohol, were distilled off. The product contains acid.
U.S. Pat. No. 2,846,459 discloses the preparation of brominated alkyl silicates by transesterification, wherein the examples proceeded from ethyl polysilicate and the latter was reacted, inter alia, with a mixture of 2,3-dibromopropan-1-ol and 2-ethylhexanol. Catalysts used here were sodium methoxide or a mixture of sodium methoxide and potassium carbonate. Here too, the compounds that were still volatile after the reaction, such as lower alcohol, were distilled off and hence corresponding brominated alkyl silicates were obtained.
Example 7 of EP1035184A1 discloses the reaction of 100 g of ethyl silicate with 18 g of 2-ethylhexanol in the presence of sulphuric acid as catalyst. The reaction was effected over 1 hour at 120° C. The volatile constituents still present thereafter were distilled off. This afforded an alkyl silicate that still had a content of 94 mol % of ethyl and a molecular weight of 1750 g/mol. Only partial transesterification was effected here with a low yield, and the product, furthermore, is acidic because of the residual amount of sulphuric acid used and remaining in the product. The product was processed further in THF.